Implement shader caching

* Shader compilation is now cached. Subsequent loads take less than a millisecond.
* Improved game, editor and project manager startup time.
* Editor uses .godot/shader_cache to store shaders.
* Game uses user://shader_cache
* Project manager uses $config_dir/shader_cache
* Options to tweak shader caching in project settings.
* Editor path configuration moved from EditorSettings to new class, EditorPaths, so it can be available early on (before shaders are compiled).
* Reworked ShaderCompilerRD to ensure deterministic shader code creation (else shader may change and cache will be invalidated).
* Added shader compression with SMOLV: https://github.com/aras-p/smol-v

servers/rendering/renderer_rd/renderer_compositor_rd.h

@@ -118,6 +118,6 @@ public:
 
 	static RendererCompositorRD *singleton;
 	RendererCompositorRD();
-	~RendererCompositorRD() {}
+	~RendererCompositorRD();
 };
 #endif // RASTERIZER_RD_H